This invention relates to liquid fertilizer, more specifically, solutions of ammonium sulfate, ammonium nitrate and urea in water which have a salt-out temperature below 32.degree. F. (0.degree. C.), yet have enhanced food value at an economical cost.
Urea-ammonium nitrate solutions (hereinafter sometimes UAN) have grown to dominate the nitrogen solutions market in the United States. Essentially three analyses have found favor. A given analysis will predominate in a geographical area because of compatibility of its salt-out temperature with regional temperature patterns. A 32 percent nitrogen UAN is dominant in the warmer South and Gulf Coast. The eastern region utilizes a 30 percent nitrogen UAN. In the colder corn belt and northern plains a 28 percent UAN is most common.
As seen in Table 1, all three analyses have a nominal 1.29 ammonium nitrate to urea (AN/U) weight ratio because, at any given salt-out temperature, this combination offers the highest solubility and highest nitrogen analysis. Approximately half of the nitrogen is derived from urea and the remainder from ammonium nitrate. The nitrogen content of these UAN solutions is far greater than can be practically obtained from either component alone.
In recent years considerable interest has developed in addition of other nutrients to nitrogen solutions, especially sulfur. Much of this sulfur has been supplied by ammonium thiosulfate (20-0-0-26S) (N-P-K-S). Ammonium thiosulfate can be mixed readily with UAN in the ratios normally desired. Even though it works well there is interest in other sources of sulfur for solutions for two reasons; 1. cost of sulfur in ammonium thiosulfate, and 2. only one-half of the sulfur is in sulfate form (desirable as plant food).
Ammonium sulfate overcomes these disadvantages, and the combination of it with urea, and ammonium nitrate is the subject of this invention.
The solubility diagram (FIG. 1) shows the combination of ammonium sulfate (AS) and ammonium nitrate (AN) which gives the highest percent solids at 32.degree. F., contains 46 percent AN and 10 percent AS for an analysis of 18-0-0-2.4S. This level of plant food is too low to be useful.
When ammonium sulfate is used in combination with urea as shown in FIG. 2, it is possible to obtain a higher analysis of 20.5-0-0-6.5S with 32.degree. F. (0.degree. C.) salt-out temperature when AS is 28 percent and urea is 32 percent; but the ratio of N to S is too low and total plant food content is still lower than for any of the UAN solutions.
Solubility data exist for a UAN-ammonium sulfate system (FIG. 3). It is possible to prepare high nutrient content solution (28-0-0-2 and 26-0-0-2.5) with 32.degree. F. (0.degree. C.) salt-out temperatures from UAN 32 and ammonium sulfate. However, this salt-out temperature is not adequate for the colder regions. We therefore sought to find the combinations of urea, AN and AS which provide the lowest salt-out temperature for a given analysis.